Well, I didn't make it home, and I'm waiting for a tow. But the good news is, I cleared the misfire code this morning, and it didn't come back in what little driving I was able to do. Maybe 40 miles total.

Can't see a leak, and the radiator and surge tank are both full. After I shut it off, it did push some water out of the surge tank.

The cap and thermostat are both less than a week old. The water pump is maybe 3-4 years old. Maybe that's it? The only times I've had failures with them would be when the seal at the impeller would go, and leak out water as fast as you poured it in. Don't know if they can fail without leaking.

 

So, time for an update.

Did a compression test, both wet and dry. The numbers were good, dry all were in the 150 psi range; wet, around 165. Not more than 10-15 psi difference between lowest and highest.

Also checked for exhaust gases in the coolant. The fluid never changed color, but it's several years old. Don't know if the stuff ever goes out of date.

Also checked the new thermostat, and it checks out ok. Even without it, the truck got up to 225* before I shut it off.

I did notice some bubbles in the radiator when I was running it without the thermostat and would rev it up. Kinda makes me doubt the block tester.

I did notice what looked like small blockages in the radiator, though. Some of the openings were "split streaming", and one I could see a small chunk of crap in the opening. The radiator is only about two years old, but maybe that's my problem.

 

Just dropped the 2000 Blazer off at the repair shop.
$ 850 estimate, but I can't do it myself, and the truck is
running fine otherwise..... ( sigh )

 

I just did the intake manifold on my blazer. get the felpro kit with all new gaskets for valve covers, intake, distributor, plenum, spider, throttle body, and new o rings.

I bought the GM service manuals (3 book set) for my 98 blazer and they are well worth the $80 I paid for them on Ebay. This will walk you through the whole procedure step by step. It was a big job but running again. Make sure you put the engine top dead center when realigning the distributor.

 

So, another update.

I rented a block tester, since the one I had began leaking the fluid out of the bottom about as fast as I could pour it in. It checked out ok, so I began to suspect the radiator.

While there was flow across it, it seemed kinda weak. Plus, it looked all gunky inside. So, new radiator. Flow is much improved, but it still overheats. As a reminder, I've got a new cap, and a new 180* thermostat, also.

Used the block tester again several times, and it always checks out good. I jacked up the passenger front and ran it till the thermostat opened to get out any air.

If I just let it idle, it will run at ~189 until I get tired of watching it. Bump the rpm to around 2k, the temp starts climbing.

Same thing driving it. Raise the rpm, the temp starts climbing.

This thing is driving me insane! If anyone has any ideas, I would love to hear them. I'm about to start pulling the heads, since I'm out of ideas.

 

Fan clutch working properly?
a/c condenser clogged up with stuff restricting air flow through the radiator?

 

The fan clutch seems to be working. It's got that "roar" when you first start it up cold. I looked at the condenser, and it seems clean as well.

I'm thinking it isn't air flow related, just from the fact that at idle and low engine speed, below 2000, it doesn't overheat. Seems like air would be more critical when the truck is stopped, verses driving and having a 40+ mph headwind.

 

Cleburne - Somewhere on this forum I think I remember reading something about intake gaskets being installed backwards and covering a water port and overheating at rpm's above idle - It might be worth a search and see if I remember right - Also IMHO i would think your heads and head gaskets are fine as compression test and no ex gas in cooling system test showed good

 

I remember reading something like that too but I cant find it.

 

Yup I looked also with no luck - I think it had something to do with installing the right hand gasket on the left side and the left hand on the right - Quite a while back so I don't remember for sure